Constant speed driven continuous rolling mill

ABSTRACT

A continuous rolling mill having tandem stands driven by constant speed motors is described wherein the pattern of roll gap of a downstream stand is adjusted as a function of the measured drive power of the adjacent upstream stand or stands. Prior to threading, all gaps are preset for the drafting schedule in a conventional manner, manually or automatically, with recognition of usual parameters such as stand temperatures, roll diameters, and the width, thickness, temperature and physical characteristics of the incoming metal. Each gap except that of the first stand is automatically adjusted, if necessary, an instant after its threading as a function of measured drive power change or changes at the preceding stand or stands caused by its threading. Adjustment maintains interstand tension or compression at near-zero value to inhibit reduction in metal width or mill cobble. Drive power measurement of each stand after the mill is completely threaded results in periodic vernier gap adjustments to maintain acceptable power distribution between stands. As applied to hot strip steel roughing mills, and particularly as applied to the last few stands, the system makes possible a combination of tandem arrangement and AC synchronous motor drive, matching conventional mill capability but using simpler electric equipment of substantially lower first cost which can be accommodated by a smaller mill building.

Unite Maxwell States Patent 1 Oct. 2, 1973 l l CONSTANT SPEED DRIVENCONTINUOUS ROLLING MILL Hugh S. Maxwell, Wichita, Kans.

Primary ExaminerMilton S. Mehr AttorneyJohn .l. Kissane et al.

[57] ABSTRACT A continuous rolling mill having tandem stands driven byconstant speed motors is described wherein the pattern of roll gap of adownstream stand is adjusted as a To a: 61 R2 function of the measureddrive power of the adjacent upstream stand or stands. Prior tothreading, all gaps are preset for the drafting schedule in aconventional manner, manually or automatically, with recognition ofusual parameters such as stand temperatures, roll diameters, and thewidth, thickness, temperature and physical characteristics of theincoming metal. Each gap except that of the first stand is automaticallyadjusted, if necessary, an instant after its threading as a function ofmeasured drive power change or changes at the preceding stand or standscaused by its threading. Adjustment maintains interstand tension orcompression at near-zero value to inhibit reduction in metal width ormill cobble. Drive power measurement of each stand after the mill iscompletely threaded results in periodic vernier gap adjustments tomaintain acceptable power distribution between stands.

As applied to hot strip steel roughing mills, and particularly asapplied to the last few stands, the system makes possible a combinationof tandem arrangement and AC synchronous motor drive, matchingconventional mill capability but using simpler electric equipment ofsubstantially lower first cost which can be accommodated by a smallermill building.

11 Claims, 4 Drawing Figures FROM 60 FROM 19 k PREDICTED ROLL FORCElSwlTCHlNG FROM 29 l CKT FROM 26 onu TO 6l PR ED lCTED ROLL FORCEPAIENIEDHBH 3L7$2.194

SHEET 3 BF 3 MEASURE ROLL FORCE IS SLAB BETWEEN NO ROLLS YES CALCULATEROLL FORCE 7 COMPARE ADJUST SCREW DRIVE OF NEXT 3 STAND MEASURE ANDSTORE DRIVE MOTOR POWER IS SLAB 1N NEXT NO STAND YES MEASURE DRIVE MOTORPOWER &

COP! PARE THIS MEASUREMENT WITH STORED VALUE DRIVE SCREWS OF IMMEDIATELYSUCCEEDiNG- STAND TO RETURN POWER TO STORED VALUE FiG. 4

CONSTANT SPEED DRIVEN CONTINUOUS ROLLING MILL This invention relates toa novel continuous tandem rolling mill and to a method of controllingthe flow of material through such mill. In a more particular aspect, theinvention relates to a continuous tandem rolling mill wherein variationsin power to the constant speed drive motor of an upstream stand areutilized to adjust the roll position of the immediate downstream stand,if necessary, to obtain low tension in the strip being rolled followingthreading at the downstream stand.

Continuous tandem rolling mills, i.e., mills wherein a strip of materialbeing rolled simultaneously extends through a plurality of rollingstands, typically are driven by adjustable speed DC motors to permitalteration of the drive motor speed at a stand upon a sensing of tensionin the rolled metal between mill stands. Because of the significant costof adjustable speed motor drives relative to constant speed motordrives, rolling mills often have attempted to utilize constant speedmotor drives for the rolling stands wherever possible. Tension, however,can build up in the metal being rolled in a tandem constant speed millresulting in an undesired reduction in metal width, or compression canincrease tending to produce cobbles in the rolled metal. Tension orcompression of thick material is difficult to measure. Constant speedmotor drives for mill stands, therefore, normally have been utilizedonly in roughing mills wherein the mill stands can be spaced by adistance permitting one piece of metal to pass through only one stand ata time. Such spacing of the mill stands, however, occupies a largeamount of factory floor space leading to proposals that adjustable speeddrives be utilized for the penultimate stand in a constant speedroughing mill to permit close spacing of the last two stands by speedcontrol of the DC drive motor for tension regulation. Hybrid AC-DCtandem mills of the foregoing type, however, are more expensive than acompletely constant speed driven mill and significant floor space isrequired between the two-stand hybrid mill and the preceding AC singlestand mill.

Although the general concept of adaptive threading, i.e., the adjustmentof predetermined set-up parameters for a downstream rolling mill standin view of measured variations from predicted values observed duringthreading of an upstream stand, is known (e.g., one system of adaptivethreading is described in my US. Pat. No. Re 26,996, re-issued Dec. 8,1970), previous mills employing adaptive threading techniques normallyhave employed DC drives for the rolling stands and loopers ortensiometers between stands to measure tension. Not only are DC drivesrelatively expensive (as was heretofore mentioned), but loopers sized toaccommodate the stiffness and weight of an interstand length of slab aremassive and also expensive with a requirement of considerable spacebetween stands for looper installation and maintenance.

It is therefore an object of this invention to provide a continuoustandem rolling mill completely powered by constant speed drive motors,without loopers or tensiometers.

It is also an object of this invention to provide an inexpensivecontinuous tandem rolling mill occupying limited floor space.

It is a still further object of this invention to provide a noveladaptive threading roll gap control system for tandem stands of acontinuous mill driven by constant speed drive motors.

It is a still further object of this invention to provide a novel methodof rolling sheet material in a continuous tandem rolling mill powered byconstant speed drive motors.

These and other objects of this invention generally are achievedutilizing a roll gap control system wherein the change in drive power toa substantially constant speed drive motor of a rolling mill stand asthe next downstream stand is threaded is observed to adjust the rollposition of the downstream stand to compensate for the observed powerchange. Thus, the method of reducing the thickness of a strip or slab ofdeformable material in accordance with this invention generally includesdriving each of at least two consecutive stands in a multi-standcontinuous rolling mill with subtantially constant speed motors andmeasuring power to the drive motor of the upstream stand of theconsecutive stands to measure deviation from a given reference level inpower to the motor upon threading of the strip material through theimmediately adjacent downstream stand. The rolls of the downstream standthen are adjusted in response to the measured deviation in power to theupstream stand drive motor to maintain the power to the upstream motorat a predetermined relationship relative to the reference level.Preferably, the roll force at the upstream stand also is measured topermit an initial coarse adjustment of the rolls of the downstream standin response to an observed deviation in the roll force at the upstreamstand from a predicted value during threading of the upstream stand.

Although this invention is described with particularity in the appendedclaims, a more complete understanding of the invention may be obtainedfrom the following detailed description of various specific embodimentsof the invention when taken in conjunction with the appended drawingswherein:

FIG. 1 is a simplified illustration of a continuous tandem constantspeed driven rolling mill in accordance with this invention,

FIG. 2 is a simplified illustration of a preferred continuous tandemrolling mill wherein a computer is utilized to supervise rolling inaccordance with this invention,

FIG. 3 is a flow chart illustrating use of the roll force at an upstreamstand to coarsely adjust the roll opening of the immediately downstreamstand prior to threading of the strip through the downstream stand, and

FIG. 4 is a flow chart illustrating the use of drive motor power changeat the upstream stand to precisely adjust the roll opening of thedownstream stand subsequent to threading the strip through thedownstream stand.

A continuous rolling mill 10 in accordance with this invention isillustrated in FIG. 1 and generally includes three tandem rolling standsR3, R4 and R5 which may form the last three stands of a roughing millutilized to incrementally reduce the thickness of slab SL. Typically,rolling stands R3-R5 are preceded by a spaced out vertical scalebreaker, a horizontal scale breaker and the first two stands of theroughing mill. However, since the length of slab SL in the scalebreakers and first two stands of the mill normally is not excessive,these preceding stands generally are situated at conventionally spacedapart locations along the mill and only roughing stand R2 of thepreceding stands therefore is shown in FIG. 1 for clarity. Each oftandem rolling stands R3, R4 and R are driven by substantially constantspeed motors DM3, DM4 and DM5 with the mass flow of material throughstand R4 being essentially matched to mass flow thru R3 followingthreading of R4 and with the mass flow of material through stand RSessentially matched to the mass flow thru R4 following threading of R5by detecting a deviation from a reference level in power to the drivemotor of the adjacent upstream stand and making an automatic roll gapadjustment. For example, upon measurement of change from the referencelevel of power to motor DM3 of stand R3 as the immediately adjacentdownstream stand R4 is threaded with slab SL, the screws SC4 ofdownstream stand R4 are adjusted by an amount to produce the requiredchange in gap to return power to drive motor DM3 to the reference level,within acceptable tolerance. It is apparent that constant mass flow fromeach stand of a tandem combination of stands imemployed. Thesubstantially constant speed drive motors are geared to the work rollsthrough suitable reduction gearing GR3-GR5 to produce the roll surfacespeed necessary to roll slab SL at a desired rate. Typically, a gearratio of approximately 16:1, :1 and 6:1 can be utilized to drive standsR3, R4 and R5, respectively.

To initiate rolling, the mill schedule required to produce the desiredoutput gage in slab SL is calculated from the known dimensions of theslab'entering the mill, the temperature of the slab and the knownmetallurgy of the slab utilizing known mass flow principles such as areset forth in detail in my heretofore cited Reissue Pat., No. 26,996,issued Dec. 8, 1970. For exam- TABLE 1.-LAST 3 STANDS, CLOSE-COUPLEDROUGHER SCHEDULE Incoming tl1ickness=4.3"

wherein M is the mill spring modulus, and k is the mean yield stress ofthe material being rolled.

plies a constancy of interstand tension or compression. By providingroll gap adjustment insuring zero or nearzero interstand tension, theinitial rolling operation will have essentially constant mass flow ateach stand.

The mill configuration includes conventionally structured rolling standswith each tandem stand being formed of upper and lower work rolls WR andbackup rolls BR to reduce the thickness of slab SL as the slab passesthru the gap between the confronting work rolls. Load cells LC3-LC5 areemployed under the bottom backup roll checks of each rolling stand tomeasure the roll force at the stand while screw drives SD3-SD5, e.g.,commercially available 200 hp, 1,030 rpm, 460 volt drives with an SCRsupply and a magnetic clutch, are located at opposite ends of each rollto rotate screws SC3-SC5 through an angle required to position the workrolls of the respective stands at a location to reduce the slab by apredetermined amount in each stand. The continuous tandem rollingstands, R3-R5, are spaced relative to each other by a distance such thatslab SL extends between at least two consecutive stands, e.g., betweenstands R3-R4, during a typical rolling schedule with the standsillustrated in FIG. 1 being spaced by a distance such that the slabsimultaneously extends between the last three stands of the tandem mill.

Drive motors DM3-DM5, in accordance with this invention, aresubstantially constant speed drive motors, i.e., motors exhibiting lessthan 1 percent speed change over the load range anticipated afterthreading of slab SL. Preferably, each of the drive motors aresynchronous motors in a horsepower rating, i.e., 10,000 hp, required todrive the work rolls although any AC motor exhibiting a limited speeddrop with load also can be The screws of the stands then are adjusted toproduce the desired thickness at each stand taking into considerationthe stand stretch (as determined in conventional fashion fromempirically derived curves depicting the variation of mill stretch withroll force).

Shortly after slab SL has entered stand R3, the roll force at the standis measured by load cell LC3 and the measured roll force is compared incomparator circuit 25 with a signal from potentiometer circuit 15corresponding to the predicted roll force as calculated for the stand(e.g., using techniques such as are described in my heretofore citedreissue patent or in US. Patent Application Serial No. 200,400 entitledComputer Controlled Rolling Mill filed November 19, 1971 in the name ofL.W. Spradlin and assigned to the assignee of the instant invention), todetermine the difference therebetween. This force difference signal thenis utilized to adjust screws 8C4 at the next succeeding stand. Becauseonly a single adjustment of screws 8C4 is required to compensate forvariations between calculated force and actual force, inhibit circuit 26is placed between comparator circuit 25 and the screw drive for thedownstream stand. The inhibit circuit is triggered to pass a singlescrew adjust signal only after sensing or entry of the head end slab SLinto stand R3 (as deter mined by differentiator circuit 27 and thresholddetector 28) and a delay, e.g., for 0.3 seconds, in delay circuit 29 togive the synchronous motor oscillations and the mill mechanicalvibrations which occur at the instant of threading an interval of timeto attenuate and to assure that the portion of the slab passing the rollgap is sufficiently beyond the head end to be full width, to produce anaccurate roll force reading. A bistable switching circuit 24 is situatedbetween threshold detector 28 and delay circuit 29 to trigger inhibitcircuit 26 only on alternate signals from the delay circuit therebypreventing adjustment of the screws as the tail of the slab leaves thestand (as will be more fully explained hereinafter).

Power to drive motor DM3 is measured by a power transducer PT3 whichproduces an output signal which is stored within power storage circuit31 upon activation of the storage circuit a fixed interval after theslab hasentered the roll gap of stand R3. To accomplish this, the outputsignal from delay circuit 29 can be utilized to trigger storage circuit31 to store a signal proportional to power to drive motor DM3 with slabSL between work rolls WR prior to threading the forward end of the slabthrough the work rolls of stand R4. The stored value of power to drivemotor DM3 then is compared in comparator circuit 36 to the power to thedrive motor after threading of stand R4 to produce a difference signalwhich is fed to screw drive SD4 (through bistable switching circuit 30switched to a closed position by the output signal from delay circuit29) to continuously adjust the screws at stand R4 by an amount necessaryto return power to DM3 to the stored reference level, within acceptabletolerance. An amplifier cricuit 61 also is utilized in the powerscrewdown control circuit to adjust the amount of screw position changefor a given power change. Because difference in the power to drive motorDM3 before and after threading of stand R4 results primarily fromtension or compression in slab SL between the threaded stands,adjustment of the screws at the downstream stand to return the drivepower at the upstream stand to, or nearly to, the power level prior tothreading of the slab into the downstream stand assures return tosubstantially zero tension in the slab.

Similarly, the deviation between predicted roll force at stand R4 andthe actually measured roll force at the stand a short interval afterthreading of stand R4 (and prior to threading of stand R5) is fedforward to screw drive SDS to adjust the screws at stand R5 prior toarrival of slab SL at stand R5. Power to drive motor DM4 also ismeasured by transducer PT4 and stored within storage circuit 41 to besubsequently compared with power to the drive motor after threading ofstand R5 in comparator circuit 46 to obtain a difference signal which isapplied to screw drive SDS to adjust the work rolls at stand R5 by anamount to return the power to drive motor DM4 to, or nearly to, theoriginal level prior to threading of stand R5.

As the tail end of slab SL leaves stand R3, load cell LC3 will produce arapidly decreasing output signal which is detected by differentiator 27and threshold detector 28 to switch bistable switching circuit 24 to analternate mode, negating triggering of inhibit circuit 26 to blockfurther adjustment of the screw drives of stand R4. The output signalfrom threshhold detector 28 also serves to trigger bistable switchingcircuit 30 to an open position, negating further change in screw driveSD4 by comparator circuit 36. Similarly, the output signal from loadcell LC4 upon passage of the tail end of slab SL from the stand isdetected by differentiator 47 and threshhold detector 48 to activateswitching circuit 40 preventing any further correction of the screwdrives of stand R5.

Unexpected time delays in slab travel between R2 and R3, resulting inthreading at lower slab temperature, requires some reduction of presetgaps to maintain the original drafting schedule, and because of theincreased resistance of the slab to deformation, may require greaterscrew position change for a given amount of gap change after threading.Accordingly, the time required for the head end of slab to travel fromrougher R2 to the initial tandem rougher stand R3 is measured, e.g., bythermal sensing devices Ti and T2 situated at longitudinally spacedlocations along the path of the slab between roughing stands R2 and R3,to produce a time difference signal from timing circuit 60. This time.

difference signal is utilized to adjust the preset gap of R3 prior toits threading and is also utilized to adjust, if necessary, theamplification of the signals from comparator circuits 36 and 46, e.g.,by altering the amplification factor of amplifier circuits 61 and 62,respectively, using empirically or mathematically determinedrelationships of elapsed time to temperature, temperature to yieldstress, yield stress to roll force and roll force to screw positionchange per unit of gap change to establish the quantitative adjustments.

A particularly preferred embodiment of this invention is shown in FIG. 2wherein computer C, e.g., a general purpose digital computer or a storedprogram computing device, is utilized both to calculate the initialrolling schedule for slab SL in the entire roughing mill and to adjustthe screws at stands R3-R5 in accordance with this invention. Thus, thecomputer initially is fed information by the operator concerning theslab, such as the slab dimensions upon entering the roughing mill, thedesired output thickness from stand R5 and the metallurgy of the slab.The computer then calculates a rolling schedule and signals are sent outfrom the computer to the screw drives to produce the desired reductionin the slab at each stand. As slab SL exits rolling stand R2, thetemperature of the slab (as measured by pyrometer P) is fed to computerC to permit an adjustment of the screws at each downstream stand shouldthe temperature of the slab vary from the predicted temperature for theslab. The output signals from thermal sensing devices T1 and T2 also arefed to computer C to permit the computer to calculate the transit timefor the slab from stand R2 to stand R3, calculate resulting temperaturerundown and calculate and send a signal to SD3 to reduce R3 gap inanticipation of threading the colder slab. Similarly, the roll force ateach stand, as measured by load cells LC3LC5, and the powers tosubstantially constant speed AC drive motors DM3-DM5, as measured byPT3PT5, are fed to the computer to permit further adjustment of the rollgap of the first AC stand after threading if desired, adjustment of rollgaps of downstream stands during threading to obtain near-zerointerstand tensions, and later minor adjustment of any or all gaps tomaintain acceptable power distribution between the several stands.

As can be seen from the flow chart of FIG. 3, roll force at stand R3 iscontinuously measured by load cell LC3 and a determination is made bythe computer whether the slab is between the rolls of the stand by, forexample, detecting a large increase in the output signal from the loadcell. When this increase in signal is observed, the measured roll forceis compared to the calculated roll force for the stand. Any discrepancybetween the actually measured roll force and the calculated roll forcethen is compensated for by adjustment of the screw drive SD4 at stand R4in accordance with the equation:

A S k'Ah l/Mf(AF) wherein 'AS is the screw adjustment produced by thescrew drive,

k is a scaling factor, greater than one,

A is the adjustment in the loaded roll gap to be produced by the screwadjustment, essentially equal to the adjustment in delivery thickness ofmaterial rolled,

M is the mill spring modulus, and p AF is the difference bitvefi'tfimeasured and the calculated roll forces.

The power to drive motor DM3 of stand R3, as determined by transducerTR3, also is fed to computer C and the computer continuously iteratesthe measurements, as shown in FIG. 4, until the presence of slab betweenthe rolls of the stand is observed, e.g., by a rapid change in the inputpower to the drive motor. After the initial observation of slab betweenthe rolls and a delay of approximately 0.3 second to enable the slab tobe completely within the gap without threading into stand R4, themeasured drive motor power is stored within computer C. This storedpower then is retained and compared with a measured power to DM3 afterthe slab threads through stand R4 to produce a difference signal whichis employed to adjust the screws SC4 of stand R4 to return the measuredpower of motor DM3 to the stored level, within acceptable tolerance.Similarly, the power to the drive motor of stand R4 is measured prior tothreading of the slab through stand R5 to provide a reference signal towhich a measured power to drive motor DM4 after threading is compared topermit adjustment of screw SCS to maintain power to drive motor DM4 atthe stored level, within acceptable tolerance.

If steady state interstand tension is represented as 1.0, the increasefrom zero at the instant of threading the second stand is exponential inpattern, in the order of wherein e is the natural logarithm,

! is elapsed time in seconds,

V is a variable, less than 1.0, dependent on many rolling parametersincluding draft and tension, and

T is slab transport time between stands.

Assuming a stand spacing of centerline to centerline, and (Table 1) aslab speed of 338 fpm between R3 and R4, the transport time isapproximately 3 seconds. As an example of potential improvement inproduct rolled, if a constant value of 0.1 is assigned to V (forillustration), tension will increase to approximately 637. of finalvalue in one time constant VT, which is 0.3 seconds, but requiresapproximately three time constants or 0.9 seconds to closely approachsteady state value.

The computer anticipates the steady state value by receiving a number oftime-based power measurements from PT3, e.g., one every 0.01 second, foras short an interval as found practical for a particular installation,thereby identifies the applicable (modified exponential) curve of astored family of curves (or their mathematical equivalent), and thenidentifies its steady state value.

The computer then calculates and sends an appropriate signal for vernieradjustment of R4 gap. In practice, the gap adjustment is completed andtension is reduced to near zero value before the slab threads R5. Theearly cutoff of tension increase avoids reduction in slab width.

Assuming l5 spacing R4-R5 the transport time R4-R5 is approximately 2seconds. It is desirable that the measurement and adjustment becompleted within this time interval, prior to the threading of R5, sothat R3 is undistrubed by the threading of R5.

0 While various specific embodiments of this invention have beendisclosed, it will be apparent to those skilled in the art that manyvariations may be made in these embodiments without departing from thebroad scope of the invention.

For example, the adaptive threading feature could be utilized by aspecialized, inexpensive, three-stand cold rolling mill for sheetmaterial equipped with induction motor drive and used for rolling sheetproduct to thinner gages. Although constant speed drive forces threadingat run speed, such operation yields high tonnage and a range of outputthickness is obtainable by using various combinations of stands, bychanging draft in the first stand used, and by changing work rolldiameters in combination with change in draft in one or more stands.

What I claim as new and desire to secure by Letters Patent of the U.S.is:

1. In a method of reducing the thickness of a strip of deformablematerial by passing said material through a plurality of tandem rollingstands forming a continuous rolling mill wherein said strip isincrementally reduced in thickness by pre-determined amounts from aninitial entry thickness to a final desired thickness, the improvementcomprising driving each of at least two consecutive stands in said millwith substantially constant speed motors, measuring power to the drivemotor of the upstream stand of said consecutive stands, detecting apower deviation to the drive motor of said upstream stand from a givenreference power level after threading said strip through the rolls ofthe immediate downstream stand and automatically adjusting the roll gapof the downstream stand in response to the detected power deviation fromsaid reference level.

2. A method of reducing the thickness of strip according to claim 1wherein the reference level of power to said upstream stand is the powerto said stand with the strip between the upstream stand rollsimmediately prior to threading of said strip into the downstream stand.

3. Arnethod of reducing the thickness of strip according to claim 2further including inhibiting further adjustment of the roll gap of saiddownstream stand upon detection of the tail end of said strip leavingsaid upstream stand.

4. In a method of reducing the thickness of a strip of deformablematerial by passing said strip through a plurality of tandem rollingstands forming a rolling mill to incrementally reduce the stripthickness by predetermined amounts from an initial entry thickness to apre-determined final desired thickness, the improvement comprisingdriving each of two consecutive stands of said mill with synchronousmotors, detecting the power to the synchronous motor drive of theupstream stand with said strip in said stand prior to threading of saidstrip between the rollers of the downstream stand, measuring the changein drive power to said upstream stand motor upon threading of said stripthrough said succeeding stand and adjusting the roll gap of thesucceeding stand by an amount which is a function of the measured changein power to the drive motor of said upstream stand.

5. In a method of reducing the thickness of a strip of deformablematerial by passing said strip through a plurality of tandem rollingstands forming a continuous rolling mill to incrementally reduce thestrip thickness in pre-determined amounts from an initial entrythickness to a final desired thickness, the improvement comprisingdriving each of two consecutive stands of said mill with substantiallyconstant speed drive motors, detecting the roll force at the upstreamstand and the power to the substantially constant speed drive motor ofsaid upstream stand, determining the difference between predicted andmeasured roll force at said upstream stand, initially adjusting the rollopenings of the downstream stand by an amount which is a function of thedetected difference in roll force at said upstream stand andsubsequently adjusting the roll gap of the downstream stand by an amountwhich is a function of the measured change in power to the drive motorupon threading of said downstream stand with said strip.

6. A method of reducing the thickness of a strip of deformable materialaccording to claim wherein said substantially constant speed drivemotors are synchronous motors.

7. A continuous rolling mill for reducing the thickness of deformablematerial comprising a plurality of rolling stands, adjacent stands beingspaced by an interval less than the length of strip to be rolled by theupstream stand, substantially constant speed drive motors driving eachof said adjacent stands, means for measuring power to the drive motor ofthe upstream stand of said adjacent stands, means for detecting adeviation in power to the drive motor of the upstream stand from apredetermined reference level upon threading of said strip through thedownstream stand, and means for adjusting the screws of the downstreamstand of the adjacent stands in response to a detected deviation fromsaid reference level in power to said upstream drive motor to obtain lowinterstand tension or compression in the material.

8. A continuous rolling mill according to claim 7 wherein said referencelevel is power to the upstream stand with the strip between the upstreamstand rolls prior to threading of said strip into the downstream stand.

9. A continuous rolling mill according to claim 7 wherein said constantspeed drive motors are AC synchronous motors.

10. A continuous rolling mill according to claim 7 wherein the onlymonitoring of the rolling operation for maintaining acceptable levels oftension or compression of metal between stands subsequent to threadingis provided by AC power transducer measuring AC motor input power, theoutput of said transducers being fed to a digital computer controllingscrew position regulators for roll gap adjustment.

11. A continuous mill according to claim 7 with an anticipatory gapadjustment feature wherein a computer repeatedly samples the drive powerof a stand motor as the next downstream stand threads, predicts themagnitude of steady state interstand tension during initial change fromzero value, calculates the change in gap at the downstream standrequired to restore nearzero tension, and initiates Vernier screwposition change of required magnitude prior to threading of the nextstandv PC4050 United States Patent Office CERTIFICATE OF CORRECTIONPatentNo. 6 Dated October 2, 1973 Inventor(s) Huqh S. Maxwell It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 1, cancel "Each of" and substitute --The. Column 3, line2, after "driven" insert respectively,-. Column 3, line 65, cancel "are"and substitute --is a--. Column 3, line 66, cancel "motors" andsubstitute --motor--. Column 3, line 67, after "rolls" insert a commaColumn 4, line 5, cancel "a" Column 4, line 5, cancel "ratio" andsubstitute -ratios.

Column 4, line 47, cancel "Application Serial No. 200,400"

and substitute -3,7l3,3l3--.

Column 4, line 48, cancel "filed November 19 1971" and substitute-issued January 30, l973--.

Column 4, line 55, after "force," (second occurrence) insert --an--.

Signed and sealed this 23rd day of April 1971+.

(SEAL) Attest: v

EDWARD I I.FLETCE1UR,JR. G. MARSHALL DANE Attesting Officer Commissionerof Patents

1. In a method of reducing the thickness of a strip of deformablematerial by passing said material through a plurality of tandem rollingstands forming a continuous rolling mill wherein said strip isincrementally reduced in thickness by predetermined amounts from aninitial entry thickness to a final desired thickness, the improvementcomprising driving each of at least two consecutive stands in said millwith substantially constant speed motors, measuring power to the drivemotor of the upstream stand of said consecutive stands, detecting apower deviation to the drive motor of said upstream stand from a givenreference power level after threading said strip through the rolls ofthe immediate downstream stand and automatically adjusting the roll gapof the downstream stand in response to the detected power deviation fromsaid reference level.
 2. A method of reducing the thickness of stripaccording to claim 1 wherein the reference level of power to saidupstream stand is the power to said stand with the strip between theupstream stand rolls immediately prior to threading of said strip intothe downstream stand.
 3. A method of reducing the thickness of stripaccording to claim 2 further including inhibiting further adjustment ofthe roll gap of said downstream stand upon detection of the tail end ofsaid strip leaving said upstream stand.
 4. In a method of reducing thethickness of a strip of deformable material by passing said stripthrough a plurality of tandem rolling stands forming a rolling mill toincrementally reduce the strip thickness by pre-determined amounts froman initial entry thickness to a pre-determined final desired thickness,the improvement comprising driving each of two consecutive stands ofsaid mill with synchronous motors, detectiNg the power to thesynchronous motor drive of the upstream stand with said strip in saidstand prior to threading of said strip between the rollers of thedownstream stand, measuring the change in drive power to said upstreamstand motor upon threading of said strip through said succeeding standand adjusting the roll gap of the succeeding stand by an amount which isa function of the measured change in power to the drive motor of saidupstream stand.
 5. In a method of reducing the thickness of a strip ofdeformable material by passing said strip through a plurality of tandemrolling stands forming a continuous rolling mill to incrementally reducethe strip thickness in pre-determined amounts from an initial entrythickness to a final desired thickness, the improvement comprisingdriving each of two consecutive stands of said mill with substantiallyconstant speed drive motors, detecting the roll force at the upstreamstand and the power to the substantially constant speed drive motor ofsaid upstream stand, determining the difference between predicted andmeasured roll force at said upstream stand, initially adjusting the rollopenings of the downstream stand by an amount which is a function of thedetected difference in roll force at said upstream stand andsubsequently adjusting the roll gap of the downstream stand by an amountwhich is a function of the measured change in power to the drive motorupon threading of said downstream stand with said strip.
 6. A method ofreducing the thickness of a strip of deformable material according toclaim 5 wherein said substantially constant speed drive motors aresynchronous motors.
 7. A continuous rolling mill for reducing thethickness of deformable material comprising a plurality of rollingstands, adjacent stands being spaced by an interval less than the lengthof strip to be rolled by the upstream stand, substantially constantspeed drive motors driving each of said adjacent stands, means formeasuring power to the drive motor of the upstream stand of saidadjacent stands, means for detecting a deviation in power to the drivemotor of the upstream stand from a predetermined reference level uponthreading of said strip through the downstream stand, and means foradjusting the screws of the downstream stand of the adjacent stands inresponse to a detected deviation from said reference level in power tosaid upstream drive motor to obtain low interstand tension orcompression in the material.
 8. A continuous rolling mill according toclaim 7 wherein said reference level is power to the upstream stand withthe strip between the upstream stand rolls prior to threading of saidstrip into the downstream stand.
 9. A continuous rolling mill accordingto claim 7 wherein said constant speed drive motors are AC synchronousmotors.
 10. A continuous rolling mill according to claim 7 wherein theonly monitoring of the rolling operation for maintaining acceptablelevels of tension or compression of metal between stands subsequent tothreading is provided by AC power transducer measuring AC motor inputpower, the output of said transducers being fed to a digital computercontrolling screw position regulators for roll gap adjustment.
 11. Acontinuous mill according to claim 7 with an anticipatory gap adjustmentfeature wherein a computer repeatedly samples the drive power of a standmotor as the next downstream stand threads, predicts the magnitude ofsteady state interstand tension during initial change from zero value,calculates the change in gap at the downstream stand required to restorenezr-zero tension, and initiates vernier screw position change ofrequired magnitude prior to threading of the next stand.